Grain dryer

ABSTRACT

A batch dryer for conditioning grain having a clock driven control system including a plurality of successively activated electric circuits for regulating drying bin temperature. The successively activated circuits maintain successively lower drying bin temperature levels defined by individual termostats in each temperature regulating circuit. A clock drive controls a plurality of cam actuated switches which turn the temperature regulating circuits on and off. The control system prevents the loading of wet grain into the drying bin late in the control cycle so that all grain then in the bin has ample time for thorough drying. The purpose of the foregoing abstract is to enable the Patent Office and the public generally, and especially the scientists, engineers, or practitioners in the art who are not familiar with patent or legal terms of phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application, which is measured by claims, nor is it intended to be limiting as to the scope of the invention in any way.

United States Patent 1 51 June 5,1973

vMcClaren GRAIN DRYER [76] Inventor: Jay L. McClaren, Box 559,

Litchfield, Minn. 55355 [22] Filed: June 28, 1971 [21] Appl. No.:157,373

[52] US. Cl ..34/48, 34/56 [51] Int. Cl ..F26b 19/00 [58] Field ofSearch ..34/45, 48, 56

[56] References Cited UNITED STATES PATENTS 3,404,467 10/1968 Burghard..34/56 3,526,969 9/1970 Alms et al. ....34/56 3,636,638 1/1972 Noyes..34/56 Primary Examiner-Carroll B. Dority, Jr. Att0rney-H. DalePalmatier et al.

57 ABSTRACT A batch dryer fOrcOnditioning grain having a clock a drivencontrol system including a plurality of successively activated electriccircuits for regulating drying bin temperature. The successivelyactivated circuits maintain successively lower drying bin temperaturelevels defined by individual termostats in each temperature regulatingcircuit. A clock drive controls a plurality of cam actuated switcheswhich turn the temperature regulating circuits on and off. The controlsystem prevents the loading of wet grain into the drying bin late in thecontrol cycle so that all grain then in the bin has ample time forthorough drying.

17 Claims, 2 Drawing Figures 2? C F CLOCK i 5 1 1 A 72, A l: A MOTOR M MM M 74 m 1- T 133 798 l 104 l l fl 1' .90 102 \l \lv pan; ,1 Y Y" Ti? f592L7J /wv. 1\0 15 5/ 88 j 0 mm NE {16 11/ j T S 125 v v x 5 I T s 426 F66 107 120 34 n. T k j 114 (112 HEATER I 1 'Zbtfl rat U U 110 SYSTEMSWITCH SYSTEM E I 144 GRAIN DRYER BACKGROUND OF THE INVENTION .Thisinvention comprises a grain dryer, and more particularly, relates to acontrol system for regulating the operation of a continuously cycling,batch, grain dryer.

Most authorities agree that grain should be harvested shortly aftermaturity when. grain moisture content is approximately 26 percent.Properly timed harvesting can produce increased yields of up to percentand profit increases of as much as 50 percent. A problem arises,however, in storing most grains when their moisture contents are between27 percent because such moisture laden or wet grain spoils rapidly andcannot be effectively stored. Since most grain destined for long termstorage should have a moisture content of approximately 12 percent newlyharvested grain must be conditioned in grain dryers to remove asignificant quantity of moisture.

Although it is important that the grain moisture content be low enoughfor storage, it is equally important to the grain seller that no moremoisture than necessary be removed. Grain with a moisture contentgreater than the optimum 12 percent level receives a proportionatelylower price per bushel than properly dried grain, but grain with amoisture content under 12 percent rarely receives a higher per bushelprice. Since the moisture content significantly affects the quantity ofgrain needed to make a bushel, the moisture content should be as near 12percent as possible if the seller is to receive the largest possiblereturn on his investment. For these economic reasons it is necessary tocarefully control the amount of moisture removed from the grain.

Two principle types of grain dryers are presently available. The firstis a continuous flow dryer through which grain continually flows whileheat is applied to the grain. To control the amount of moisture removedfrom the grain, the moisture content of the grain leaving the dryer ischecked periodically, and depending on whether the moisture content ishigh or low, the grain flow rate is respectively slowed down or speededup to vary the time during which grain is exposedto heating. Theprinciple shortcoming of continuous flow dryers is that grain does notflow evenly through the dryer, and thus grain in some parts of the binhas too much moisture removed while grain in other parts has too littleremoved. The grain leaving the dryer may thus have a wide variation inmoisture content. With such wide variation, measurement of the moisturecontent of grain samples leaving the dryer can provide unreliable dataon which to determine the flow rate of the grain. For these reasons itis difficult to obtain uniformly conditioned grain with a continuousflow dryer.

The second type of grain dryer is the batch" dryer which is designed todry a load of wet grain to an appropriate moisture content, unload thegrain, then reload the dryer, and repeat the cycle. This dryertraditionally applies a single fixed temperature level to a bin ofstationary grain for a predetermined time and is theoretically capableof producing conditioned grain having a very uniform moisture content.The grain remains stationary during the cycle to eliminate much of thenonuniform conditioning associated with continuous flow dryers.

One shortcoming of the presently available batch dryers is that they donot process grain as rapidly as the continuous flow dryer. Since batchdryers operate at a single fixed temperature level, the level must besuffciently low to avoid grain damage at all times during the controlcycle. Since grain can withstand only low heat levels late in a controlcycle these dryers use the low heat level throughout the cycle. Thisresults in a long, slow, drying period.

Another shortcoming of presently available batch dryers is that theyload wet grain into the drying bin throughout the control cycle in orderto refill the drying bin as the grain already in the drying bin shrinksin response to heating. Grain shrinkage of as much as 30 percent duringconditioning is not. unusual and requires that additional grain beloaded into the bin during the control cycle if the dryer is to be: usedmost economically, Unfortunately, wet grain loaded late in the controlcycle often does not have ample time to be dried before it is unloaded.

Presently available batch dryers continue. to load wet grain at any timeduring the cycle because the bin must be kept essentially full in orderto avoid venting of the bin which greatly decreases drying efficiency. Adrying bin is ordinarily defined by inner and outer perforated wallsbetween which grain is stored and through which heated air flows. It isdesireable that the heated air meet equal flow resistance from the grainat all parts of the bin if air flow is to be uniform throughout thedrying bin. If grain shrinkage results in a section of the bin having nograin between inner and outer walls, most of the heated air will ventthrough the unoccupied section, and dryer efficiency will be seriouslyimpaired. Presently available batch dryers load wet grain into thedrying bin throughout the drying cycle to insure that no venting occursat the top of the bin.

SUMMARY OF THE INVENTION trol system with a plurality of drying bintemperature regulating electric circuits which maintain a series ofsuccessively lower temperature levels in the drying bin.

defined by thermostats in the circuits. Initially a first temperatureregulating circuit maintains a high temperature level in the drying binfor an appropriate time interval at the end of which a clock driven camactuates one or more switches, turning off the first temperatureregulating circuit and turning on a second similar regulating circuitwhich maintains a lower temperature level. Three such regulatingcircuits are used with the embodiment shown herein to establish threetemperature levels, but a greater or lesser number of heating levelscould just as readily be utilized with the inven; tion.

Ordinarily wet grain is heavily moisture laden when harvested and canwithstand a higher heat level at the beginning of a drying cycle thanlater in the cycle when relatively low amounts of moisture remain in thegrain. The evaporation of the moisture initially in the grain absorbsmuch heat which otherwise might burn or crack the grain. Later in thecycle much of the moisture has been evaporated; at that time high heatlevels can easily burn or crack the grain. It is therefore desirable touse a high heat level at the beginning of the control cycle and a seriesof lower heat levels as the control cycle progresses. Such a series oflevels dry a load of grain more rapidly than the grain dryers presentlyon the market, which have only a single heat level selected to be lowenough to avoid burning or cracking the grain late in the cycle whenmost moisture is evaporated.

' Each temperature regulating circuit when energized turns on a heaterregulator and controls the regulator, causing it to open a fuel valve apredetermined amount to establish a given heating level associated withthe particular regulating circuit. Each temperature regulating circuitwhen energized defines a successively lower heating level. When thetemperature level associated with a particular temperature regulatingcircuit is reached, a thermostat in the circuit is activated to permitthe circuit to reduce the rate at which fuel is delivered to the heaterso that the desired temperature is not exceeded. When the temperaturefalls slightly, the thermostat is again activated to increase the fuelsupplied to the heater. Each temperature regulating circuit is turned onand off at predetermined times by the clock drive which controls thetime during which grain is exposed to each temperature level.

I Grain remains substantially stationary in the drying bin during thecontrol cycle, no unloading occuring unit the full cycle is completed.This avoids the problem of uneven grain flow through the bin and resultsin processed grain with a substantially uniform moisture content.

After the three successively lower temperature levels have been used tocondition the grain, a fan circulates air to cool the grain until thegrain is unloaded. If desired, the cooling interval can be omitted andthe grain unloaded at completion of heating and cooled elsewhere.

A loading circuit controls the operation of the grain loading systemwhich includes a loading auger which distributes wet grain evenlythroughout the drying bin. The control system supplies power to theloading circuit to fill the bin with grain before heating commences andalso during a part of the control cycle. Late in the control cycle aclock driven cam opens a switch which turns off power to the loadingcircuit thereby preventing the further loading of wet grain until afterthe cycle is completed and the conditioned grain unloaded.

The grain dryer invention encounters no problems with venting at the topof the drying bin. The control system supplies adequate quantities ofwet grain to the drying bin during the control cycle so as to avoidventing. The most recently added grain drys thoroughly but does notshrink sufficiently to cause venting of the bin.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of agrain dryer with a section of the drying bin removed.

FIG. 2 is a schematic circuit diagram of the control system used withthe grain dryer of FIG. 1.

DESCRIPTION AND OPERATION OF THE INVENTION FIG. 1 shows a grain dryerwith a'frame 12 supporting a grain drying bin 14, which surrounds anddefines a central air plenum 16. Both inner wall 18 and outer wall 20 ofthe drying bin 14 are perforated to permit drying air to flowtherethrough from the plenum 16 to the atmosphere. A supply conduit 22originating at a source of grain (not shown) discharges wet grain into ahopper 23 at the top of the grain dryer 10. A loading auger 24, poweredby loading auger motor 26, extends into the hopper 23 in order to conveygrain from the 4 hopper to the drying bin and distribute it evenlythroughout the length of the bin.

An unloading auger 28, powered by unloading auger motor 30 extends alongthe bottom of the bin to an exit hopper and conduit 32 and when operatedconveys grain from the bin and into the exit conduit, which leads to astorage chamber.

A heater 34 and fan 36, located in housing 38 at the end 40 of the graindryer, generate heated air which enters the plenum l6 and exhauststhrough the perforated sides of the bin 14. The heater 34 may be of anytype capable of operation at a plurality of different heating levels; ifdesired several burners may be used to heat the air supplied to theplenum chamber or several fans used to deliver air to the shown plenum.A burner element utilizing a fluid fuel such as gas or oil issatisfactory.

A fuel valve 42 located in valve compartment 44 regulates the fuelsupplied to the heater 34 from fuel supply 46. Temperature sensingelements 48, 50, and 52 of thermostats 58, 60, and 62 (FIG. 2) areattached to the plenum side of the inner wall 18 of the bin and maintainthree successively lower drying bin temperature levels describedhereafter. A clock controlling thermostat 64 has a temperature sensingelement 54 located in the drying bin 14 on the outer wall 20 thereof andserves a purpose hereafter explained. A control system box 56 houses thegrain dryer control system, described hereafter, which permits the graindryer 10 to operate as a continuous cycle, batch dryer. Electricalinterconnections associated with the electrical components of FIG. 1 areomitted therefrom for simplification.

FIG. 2 is a schematic circuit diagram of the grain dryer control system.A conventional clock motor 66 has the clock motor shaft 68 coupled to afirst end 70 of a rotatably mounted cam shaft 73 by means of a frictionclutch 74. The cam shaft 72 has cams A, B, C, D, E, and F thereon, andalthough six cams are shown on the shaft it should be understood that agreater or lesser number of cams can be used, the number shown beingmerely illustrative of one embodiment of the invention.

It should be further understood that although only a single clock motoris shown in FIG. 1, the invention can be practiced using a plurality ofsuch motors. For example, each of the shown cams could be rotated by anindividual clock motor connected to the cam through a friction clutch.This would permit the angular displacement of each cam to beindividually varied by an operator. Use of a plurality of clock motorsis within the purview of the invention.

A solenoid operated clutch 76 exerts a restraining force on the camshaft 72 as will be further discussed hereafter. The second end 71 ofthe cam shaft 72 is coupled through a second friction clutch 78 to acontrol shaft 80 extending from time dial 82, which is accessible to anoperator. The control shaft 80 is provided with a spring loading device84 which will be further described hereafter. The clock motor 66,clutches 74, and 78, shafts 68, 72, and 80, the plurality of cams,spring loading device 84 and time dial 82 collectively form a clockdrive.

The object of spring loading device 84 is the establishment of arestoring torque to act on control shaft 80 as the time dial 82 isrotated to an appropriate position by an operator. The angulardisplacement of dial 82 determines the overall heating time of the graindryer control cycle which begins with loading of a batch of wet grainand ends with the dryer ready to load a second batch of wet grain.

Rotation of control shaft 80 does not result in immediate rotation ofcam shaft 72 because solenoid clutch 76, when energized, grips cam shaft72 with sufficient force to prevent the control shaft 80 from rotatingit. Control shaft 80 is retained in a spring loaded condition byfriction clutch 78. When the solenoid clutch '76 is de-energized, springloading device 84 rotates both control shaft 80 and cam shaft 72 to aposition at which heating of the drying bin begins and from which theclock motor will return them to their initial spring loaded conditionwhen the control cycle ends. As the cam shaft 72 is rotated the heater34 is turned on and heated air begins circulating in the bin. Ordinarilythe clock motor is not energized at this stage of the cycle.

vClutch 74 permits the cam shaft 72 to rotate in response to the torqueacting on control shaft 80 without the clock motor shaft 68 beingrotated. The clutch 74} is selected such that the clock motor cantransmit sufficient torque therethrough to cam shaft 72 to turn thecamshaft even when solenoid clutch 76 is gripping the cam shaft. Clutch78 is constructed so the rotation of cam shaft 72 by clock motor 66rotates control shaft 80 to gradually restore the spring tension on thecontrol shaft as the cycle progresses. It should be understood that theclock drive system shown is but one clock drive useable with theinvention and that other clock drives could have been used and arewithin the purview of the invention.

The control circuit shown generally at 86 is connected to an electricalpower source 88 through power switch 90 and grain supply switch 92. Theswitch 90 is a master switch to energize-and de-energize the entiregrain dryer. The grain supply switch 92 detects the presence of a supplyof wet grain to be dried. Switch 92 may be a mercury or pressure switchassembly in the hopper 23 or alternatively may be replaced by a timerarranged to turn off all power to the grain dryer when the loadingaugers run for an unnaturally long period; switch 92 may include a relaycontrolled by the mercury or pressure switch to turn the entire graindryer off when the grain supply is exhausted. .When

- grain is present in the hopper 23 the grain supply switch 92 isclosed. When the supply of grain is exhausted, the switch 92 opens toautomatically turn off the grain dryer.

Switch 92 is connected to thermal time delay relay 94 which ordinarilyis closed as shown. Conductor 96 extends from relay 94 to holding coil98 of solenoid clutch 76. The clutch 76 grips cam shaft 72 when holdingcoil 98 is energized, preventing cam shaft 72 from being rotated byspring loaded control shaft 80.

Thermal time delay relay 94 opens the terminals P-P in response to asurge of current in coil 128, and holds the terminals open for a timedelay before permitting the terminals to reclose. Relay 94 should have adelay time, during which terminals P-P are open, adequate to permitsolenoid clutch 76 to release cam shaft 72 and the cam shaft to rotatein response to spring loaded control shaft 80. A delay of l to 2 secondsis adequate. The holding coil 98 of the solenoid clutch 76 is energizedearly in the cycle as soon as the grain drying bin has been filled, aswill be described hereafter.

Conductor 100 extends from solenoid clutch 76 to single pole doublethrow switches 102, 104, and 106 which are mechanically actuated by camsA, B, and C, respectively. Each of the switches 102, 104, 106, 136, 140,and 150 have two alternative positions designated as tenninals X and Y.The positions designated as X represent the switch arrangement at thebeginning of the control cycle before a batch of wet grain is loadedinto the drying bin. As the control cycle proceeds, the switches aremoved from the X to the Y terminals, as will be described hereafter.

Switch 102 has its X terminal connected to the holding coil 105 of relay107. When holding coil 105 is energized, the relay closes a circuitbetween terminals S-S. When the holding coil 105 is de-energized therelay opens terminals SS and closes a circuit between terminals TT.

The Y terminal of switch 102 is connected to a manu ally operated singlepole double throw toggle switch 108. When the toggle switch 108 is atterminal X as shown in FIG. 2, it connects terminal Y of switch 102 to acircuit containing clock controlling thermostat 64 and relay 110. Thethermostat 64 has its temperature sensing element 4 mounted in thedrying bin 14 at the outer wall 20 thereof. Thermostat 64 forms an openswitch so long as a predetermined drying temperature T is not exceededat the outer wall of the bin. When temperature T is reached thethermostat 64 closes, and current passing therethrough follows conductor112 to energize holding coil 114 of relay 110 which closes terminals VVto complete a circuit from terminal Y of switch 102 through relay 110and conductors 1 16 and l 18 to clock motor 66. Relay 110 includescircuitry known to the art which assures that once terminals V-V haveclosed, they do not open until the control cycle has been completed andthe conditioned grain has been unloaded. Thus, even if temperature T isnot maintained during the control cycle, the clock is not stopped. Thepurpose of thermostat 64 and relay is to permit extremely wet grain tobe heated to a desired predetermined temperature so as to drive offexcess moisture and then begin a timed drying cycle.

It is sometimes desirable to carefully time the heating periods as forexample when unusually dry grains are undergoing a short conditioningperiod or when seed grains are beingprocessed. In such cases the toggleswitch 108 is moved to terminal Y disconnecting the clock controllingthermostat 64 and supplying current directly to clock motor 66 throughconductor 118.

Cam acturated single pole double throw switch 106 is shown connected toterminal X which is series connected by conductors and 121 to recycleswitch 122 and through terminals S-S of relay 107 and conductors 125 and126 to loading auger system 124.

The recycle switch 122 may be a mercury switch, pressure switch, orelectric eye located near the top of the grain bin. The switch remainsopen until the grain level reaches the switch and closes it. Once closedthe recycle switch can conduct current to conductor 127 which extends tothe heating coil 128 of thermal time delay relay 94 which responds to acurrent surge by opening terminals PP for a detennined time interval.This interrupts the current to solenoid clutch 76, releasing the camshaft 72 which rotates to a position at which heating begins.

The loading auger system 124 includes loading auger 24, and loadingauger motor 26. it may also include apparatus in the supply conduit 22for closing the conduit when the loading auger motor is off and openingthe conduit when it is on.

Terminal Y of single pole double throw switch 106 has a grain levelswitch 130 connected in series therewith. The switch 130 may be amercury switch, pressure switch or electric eye which opens the circuitwhen the level of the grain reaches the switch 130. Conductor 126extends from switch 130 to the loading auger system 124. Conductor 120,terminals 8-8 of relay 107, conductor 125, grain level switch 130, andconductors 126 and 131 comprise a grain loading circuit extending fromterminals X and Y of switch 106 to the loading auger system 124. Singlepole double throw switch 104 is mechanically actuated by cam B andsupplies power from conductor 100 to terminals X or Y of the switch.Terminal X is connected in series through terminals TT of relay 107 tounloading auger system 132. The unloading auger system 132 includesunloading auger 28 and un; loading auger motor 30. If desired it mayinclude a switch at the bottom of the grain bin which opens to turn offthe motor when the bin is empty, although this is not essential.

Terminal Y of switch 104 is connected to fan 36. The cam actuated switch104, conductor 133, and fan 36 collectively form a ventilating circuitfor the grain dryer. Connected in parallel with the fan 36 is a heatertime controlling circuit which supplies all electrical power to thedrying bin temperature regulating circuits, described hereafter. Theheater time controlling circuit includes conductor 134 and heater powerswitch 136 which is mechanically turned on and off by cam D. Switch 136is closed for a maximum time interval controlled by cam D. When heaterpower switch 136 opens, heating terminates except as described below.With the shown control circuit the heater 34 can not be operated unlessthe fan 36 is simultaneously operated. This arrangement is desirablebecause without fan operation heat builds up adjacent the heaterresulting in locally burnt or cracked grain.

Manually operated toggle switch 138 and conductor 139 provide a shuntfor the heater time controlling circuit which makes it possible tobypass the cam activated switch 136 when more rapid drying is desired aswill be described hereafter.

When either heater power switch 136 or toggle switch 138 is closed,single pole double throw switch 140, which is mechanically actuated bycam E, is electrically connected in parallel with fan 36. When switch140 is at terminal Y, a first drying bin temperature regulating circuitis energized. This first regulating circuit comprises switch 140,conductor 141, thermostat 58, and conductor 142.

The thermostat 58 has its temperature sensing element 48 located in theplenum on the inner wall 18 of the drying bin. The thermostat 58 is setto maintain a high drying temperature T, adapted to rapidly removemoisture from the initially wet grain. The most suitable temperaturedepends on the type of grain and its initial moisture content; 220 F. isan acceptable T temperature for most grains. The temperature setting ofthermostat 58 can be varied at control box 56 (FIG. 1). Thermostat 58remains closed until the temperature T, is reached and then opens. Whenclosed, current flows therethrough to heater regulator 144 which mayconsist of any known electromechanical transducer capable of openingvalve 42 predictable amounts in reponse to current reaching it throughconductors 142, 145, or 146. Cam E is constructed to keep switch atterminal Y for a predetermined time interval during which the highheating level associated with temperature T is maintained. By properlysetting time dial 82 the time can be increased or decreased.

The heater regulator selected should be a transducer capable of openingvalve 42 a plurality of different amounts in response to a plurality ofdifferent inputs. The valve 42 controls fuel flow through fuel line 47extending from fuel source 46 to the heater 34. Although the heater isshown as being a fluid fuel burner, it can be electrical.

Terminal X of switch 140 is connected to conductor 153 which comprises acircuit leading to single pole double throw switch which is mechanicallyactuated by cam F Switch 150 is connected to its terminal Y after therelease of shaft 72 by solenoid clutch 76; terminal Y is seriesconnected to thermostat 60 and heater regulator 144. The switch 150,conductor 151, thermostat 60 and conductor 145 comprise a second dryingbin temperature regulating circuit controlling regulator 144 to openvalve 42 a predetermined amount less than that caused by the firsttemperature regulating circuit. The thermostat 60 has a temperaturesensing element 50 in the plenum. Thermostat 60 is similar to thermostat58 but is set for a lower temperature T, which can be varied at .thecontrol box but which typically may be 190 F. So long as thistemperature is not reached the thermostat 60 remains closed conductingcurrent to the heater regulator to open valve 42 an amount less thanthat produced by the first regulating circuit to establish a mediumtemperature level T at the drying bin when the second regulating circuitis energized.

Switch 150, conductor 152, thermostat 62, and conductor 146 collectivelycomprise a third drying bin temperature regulating circuit. Thermostat62 has a temperature sensing element 52 element 52 attached to the innerwall 18 of the drying bin, and the temperature setting can be variedfrom the control box 56. Thermostat 62 is set for temperature T which isless than T, or T such as F. Until the temperature T is reached, thethermostat 62 remains closed, permitting current to flow therethrough toheater regulator 144 which responds by opening valve 42 an amount lessthan that produced by either of the two temperature regulating circuitsalready discussed so that heater 34 operates at a low heating level.When thermostat 62 opens, heater regulator 144 reduces fuel flow throughvalve 42, reducing the heat output of the heater.

It should be understood that only one of the three temperatureregulating circuits disclosed can control the heater regulator 144 atone time. If no current is supplied to the regulator 144 through atemperature regulating circuit, the regulator may turn off valve 42 andthereby reduce the heat produced by heater 34. It should be understoodthat even though only three temperature regulating circuits are shown,the invention can use a greater or lesser number of such circuits toestablish a greater or lesser number of temperature levels.

Although the drying bin temperature regulating circuits are referred toherein as regulating the temperature of the drying bin, it should beunderstood that the circuits measure the temperature changes at thesensing elements 48, 50, and 52 which are located adjacent the dryingbin in the plenum chamber 16 and regulate the temperature of air in theplenum. The drying bin temperature can be adequately regulated byregulating the temperature of air in the plenum because plenum air flowsfrom the plenum directly into the drying bin.

The heater regulator 144 need not turn off valve 42 so that no fuelreaches heater 34. The regulator 144 works satisfactorily if it merelyreduces the fuel flow through valve 42 when the desired temperature T Tor T has been reached and increases the flow when the temperature dropsbelow the desired temperature. The shown off on thermostats 58, 60, and62 can then be replaced by thermostats capable of producing a firstsignal when the desired temperature is reached or exceeded and producinga second signal when a lower temperature is present. The first signalcan be used to activate regulator 144 to reduce fuel flow to the heaterand the second signal to increase the fuel flow thereto.

In operation, an operator first closes the power switch 90 supplyingpower to grain supply switch 92. If a supply of grain is available to bedried, the supply switch 92 is closed as shown and current flows throughterminals P-P of thermal time delay relay 94. When thesupply of grain isexhausted, grain supply switch 92 opens, and the entire grain dryercontrol system turns off.

Thermal time delay relay 94 is ordinarily in a closed conditionconducting current across terminals P-P to holding coil 98 of solenoidclutch 76 and thence to conductor 100 which supplies power directly tocam actuated switches 102, 104, and 106. So long as holding coil 98 ofsolenoid clutch 76 is energized, the clutch restrains cam shaft 72, andtime dial 82 cannot transmit rotation to the cam shaft. After anoperator has connected the grain dryer to a power source 88, he rotatestime dial 82 to determine the time duration of the control cycle. Theangular displacement of dial 82 is proportional to the time duration.Typically the time selected may be 90 minutes, however this time can beincreased or decreased depending on moisture content of the grain andthe type of grain to be dried. It should be understood that it ispossible to quite accurately predict required drying time when theinitial moisture content of the grain is known. Rotation of dial 82causes springloading device 84 to exert a restoring torque on controlshaft 80. The friction clutch 78 connecting control shaft 80 to camshaft 72, however, prevents rotation of control shaft 80 by retainingthe shaft 80 at its spring tensioned position so long as solenoid clutch76 is energized and prevents rotation of cam shaft 72; At this point thecontrol cycle has not yet commenced and the cams on cam shaft 72 havenot yet rotated. Cam actuated switches 102, 104, 106, 136, 140, and 150are in contact with the terminals indicated as X, and clock motor 66 isturned off.

Current from conductor 100 flows through switch 102, which ismechanically actuated by cam A, to the holding coil 105 of relay 107,closing terminals SS of the relay, permitting the loading auger system124 to be operated as hereafter described. Switch 104 actuated by cam Bis also at terminal X, but since terminals T-T of relay 107 are open, nocurrent can reach unloading auger system 132 which thus remainsinactive. Since switch 104 is at terminal X, no current reaches fan 36or the heater time controlling circuit.

Switch 106, actuated by cam C, contacts terminal X, pennitting currentto flow to the recycle switch 122 through conductors 120 and 121 and tothe loading auger system 124 through terminals S--S of relay 107 andconductors 125 and 126. Since the recycle switch 122 remains open solong as the grain bin is empty no current flows through the recycleswitch to heating coil 128 of thermal time delay relay 94. Current does,however, flow to the loading auger system, and as a result grain movesfrom supply conduit 22 into hopper 23, and loading auger motor 26 isenergized to turn loading auger 24 which distributes the incoming grainevenly along the length of the drying bin. The loading continues untilthe grain reaches the level of recycle switch 122 at the top of thegrain bin and closes the recycle switch.

As the recycle switch is closed, current flows from terminal X of switch106, through the recycle switch, along conductor 127 to energize heatingcoil 128 of thermal time delay relay 94. As a result, terminals P-P openand current through relay 94 is interrupted for a short time intervalsufficient to de-energize holding coil 98 of solenoid clutch 76 causingthe clutch to release its grip on cam shaft 72. Since the cam shaft isalready spring tensioned by spring loading device 84, shaft 72immediately rotates causing the cams thereon to move to a new positionfrom which the clock motor 66 will gradually rotate them back to thestarting position. The friction clutch 74 permits the cam shaft to moveto the said new position without rotating the clock motor shaft 68. Atthis point in the cycle the clock motor is still turned off.

Rotation of cam shaft 72 moves cam actuated switches 102, 104, 106, 136,140, and 150 to their respective Y terminals, de-energizing the Xterminals. Switch 102, actuated by cam A, thus no longer suppliescurrent to holding coil 105 of relay 107, and thus relay 107 opensterminals SS and close terminals T-T. Simultaneously switch 104,actuated by cam B, interrupts current flow to terminal X, thuspreventing the unloading auger system 132 being energized even thoughterminals T-T of relay 107 are closed. Switch 106, actuated by cam C,moves from terminal X to Y, preventing current from reaching recycleswitch 122 from terminal X. Since current no longer reaches recycleswitch 122, heating coil 128 of thermal time delay relay 94 is no longerenergized, and current once again flows through conductor 96 to solenoidclutch 76, which regrips the cam shaft 72. It should be understood,however, that the solenoid clutch 76, does not exert sufficient force oncam shaft 72 to prevent the clock motor 66 from turning the cam shaftonce the clock motor has been turned on.

Switch 104, actuated by cam B, supplies current from its terminal Y tofan 36; current flows from switch 104 through conductors 133 and 134 toheater power switch 136, which is now at terminall Y. Current continuesfrom switch through conductor 141, thermostat 58 and conductor 142 toheater regulator 144. Thermostat 58 detects that temperature T, has notbeen reached and signals the heater regulator 144 which opens valve 42 apredetermined first amount sufficient to establish a first heating levelin the drying bin. This first heating level is a high level designed forrapid drying. The regulator continues to permit a high fuel flow to theheater until temperature T, is reached. The thermostat 58 then detectsthat T, has been obtained and signals the regulator 144 to reduce thefuel flowing through valve 42 by reducing the valve opening. In this waythermostat 58 and regulator 144 maintain the temperature of drying binair in a temperature range near 1",.

Fan 36 blows the heated air into plenum 16, from which it passes throughthe grain and exhausts to the surrounding atmosphere. Since the grainhas a high moisture content when loaded it can easily absorb the initialhigh heat output without damage to the grain. The dryer thus suppliesheat energy to the grain at an initially high level drying the grainrapidly when its high moisture content makes it capable of withstandinghigh temperature. The high initial heat level significantly shortens theoverall required conditioning time.

Switch 102, actuated by cam A, conducts current from conductor 100 toterminal Y and thence through toggle switch 108 to clock controllingthermostat 64 which is set for a predetermined temperature T which maybe varied by an operator. The thermostat 64 remains open, passing nocurrent therethrough until the temperature T is reached. When thistemperature T is reached, thermostat 64 closes and current passestherethrough to holding coil 114 of relay 110. In response, relay 100closes terminals V'V permitting current to flow therethrough and alongconductors 116 and 118 to turn on clock motor 66 which now beginsoperating. Terminals V-V remain closed until the clock motor is finallyturned off by switch 102 in order to assure that the timed control cycleis not interrupted once it begins.

The clock controlling thermostat 64 assures that the timed heating ofthe grain does not begin until a predetermined drying temperature T hasbeen reached. The thermostat 64 is particularly useful when the grainhas an unusually high moisture content and large quantities of heat mustbe expended before the grain at the outer wall of the bin reachestemperature T,,. In such a case, if thermostat 64 were not present, thetimed drying levels might be insufficient to condition grain. Thermostat64 prevents the timed drying period from commencing until temperature Tis reached at the outer wall 20 of the bin.

If for any reason the operator does not wish to use the clockcontrolling thermostat 64 to activate the clock motor 66, the operatormoves toggle switch 108 to terminal Y'and the clock will be energized assoon as switch 102 moves to its terminal Y when cam shaft 72 rotates inresponse to de-energized solenoid clutch 76. In grain which containslittle moisture or grain which is extremely sensitive to heat, such asseed grain, it is often helpful if the time interval during which grainis exposed to heat is completely time controlled. This is made possibleby toggle switch 108.

Switch 106 actuated by cam C, now in contact with its terminal Y,permits current to flow through conductor 131, grain level switch 130,and conductor 126, to the loading auger system 124. No current can passfrom terminal Y of switch 106 to the recycle switch 122 since terminalsSS of relay 107 have been opened.

The grain level switch 130 remains open so long as the drying bin isfull. When the grain level drops due to grain shrinkage the switch 130closes, and the loading auger system 124 is energized to load additionalwet grain into the drying bin. This additional loading step can occurduring most of the control cycle, but late in the cycle before heatinghas ended cam C turns switch 106 to terminal X to cut off power to theloading auger system. Thus no wet grain is loaded into the bin at astage in the control cycle which would leave inadequate remaining dryingtime to thoroughly condition the newly added wet grain. All grain thenin the bin will be thoroughly conditioned at the end of the cycle. Theamount of drying time for the newly added wet grain varies, of course,depending on the type of grain and its moisture content.

The grain drying bin 14 encounters no venting problem at the top thereofsince wet grain is added during much of the cycle in response to grainshrinkage. When the loading auger system 124 is finally turned ofi toprevent further loading, the remaining drying time is sufficiently shortthat the resulting shrinkage is inadequate to produce venting problemsbut still adequate to thoroughly condition the grain.

After the first temperature regulating circuit turns on the heater 34,the heating continues at the high temperature level T for apredetermined interval timed by clock motor 66. After a predeterminedtime interval adequate to significantly reduce the moisture content ofthe grain, cam E moves switch from terminal Y to X thus turning off thefirst drying bin temperature regulating circuit and conducting currentthrough conductor 153 and to terminal Y of switch which supplies currentto'the second temperature regulating circuit whichthen establishes andmaintains a medium temperature T, determined by thermostat 60 for apredetermined time. Thermostat 60 measures the temperature at sensingelement 50 and signals the heater regulator 144 to increase the fuelflow through fuel valve 42 if the temperature is less than T, anddecreases fuel flow if the temperature is greater than T Thus the second temperature regulating circuit pennits heater 34 to maintain amedium heat level near temperature T After a predetermined time intervalhas elapsed, cam F rotates sufficiently to move switch 150 from terminalY to terminal X which turns off the second temperature regulatingcircuit and energizes the third. This third temperature regulatingcircuit has a thermostat 62 which maintains a temperature level neartemperature T at the drying bin just as thermostats 58 and 60 maintainedtheir temperature levels when energized.

After a predetermined time interval elapses, cam D rotates sufficientlyto move switch 136 from terminal Y to X, which turns off all power tothe temperature regulating circuits. After switch 136 opens, heater 34provides no further heat during the control cycle.

Even through the heater is off, fan 36 continues to circulate airthrough the bin so long as switch 104 is at terminal Y. This aircirculation cools the grain prior to its being unloaded. After anadditional time period has elapsed, cam B turns sufficiently to moveswitch 104 from terminal Y to terminal X to turn off fan 36.

When a large quantity of grain is to be dried, and an outside storagebin in which the grain can be cooled is available, it is sometimeshelpful to omit the cooling period just described and transfer the grainto the outside bin for cooling. If the operator wishes to omit thecooling period, he closes toggle switch 138 which provides a shunt tobypass heater power switch 136. This results in the third temperatureregulating circuit maintaining temperature level T until carn B movesswitch 104 from terminal Y to terminal X.

When switch 104, actuated by cam B, returns to terminal X, fan 36 isde-energized and current from conductor 100 flows through switch 104 andterminals T-T of relay 107 to unloading auger system 132, turning onunloading motor 30 which activates the unloading auger 28 removing theconditioned grain from the drying bin to a storage bin.

After the elapse of a predetermined time interval adequate to unload thegrain, cam A actuates switch 102, moving it from terminal Y to terminalX, turning off the clock motor 66 and re-energizing holding coil 105 ofrelay 107 to open terminals T-T and close terminals S-S.

Switch 106, actuated by cam C, is now at terminal X permitting currentto flow through conductor 120, terminals 8-8 of relay 107 and conductors125 and 126 to loading auger system 124. The loading auger motor 26turns on and grain is again loaded into the drying bin. When the grainreaches a level adequate to close recycle switch 122, current flowsalong conductor 127 to the heating coil 128 of relay 94, and the relay94 opens terminals P-P to briefly de-energize solenoid clutch 76. Itshould be understood that the rotation of shafts 72 and 80 by clockmotor 66 during the already described control cycle restores the springtension exerted on the shaft '80 by spring loading device 84.Deenergizing solenoid clutch 76 permits the shafts 72 and 80 to rotateto the already described position at which heating begins and from whichthe control cycle repeats the already described operations andcontinually recycles so long as wet grain is available. When the grainsupply is exhausted, grain supply switch 92 opens and the controlcircuit turns off the grain dryer automatically.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made in the structure, circuitry and circuitcomponents shown herein without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:

l. A grain dryer having a control cycle for conditioning wet graincomprising:

a frame;

a grain drying bin attached to the frame to hold a supply of wet grainto be conditioned;

a heater and fan mounted to said frame to heat and circulate air throughthe drying bin;

a clock driveincluding at least one clock motor and a plurality of camsrotatably coupled to the clock motor for rotation thereby;

a plurality of drying bin temperature regulating electric circuits, eachcircuit including a thermostat and a switch actuated by one of the camsto close and open the circuit at predetermined times in the controlcycle, each regulating circuit maintaining a predetermined drying bintemperature level de .fined by the thermostat in the circuit when theswitch is closed and the circuit energized; and

a heater regulator responsive to the said regulating circuits to varyheat output of the heater so as to maintain predetermined temperaturelevels defined by the temperature regulating electric circuits;

a loading auger system for loading grain into the drying bin; and

a loading circuit responsive to said clock drive and controlling saidloading auger system to load grain into the bin during the control cycleso that additional grain is loaded as the grain in the drying binshrinks in response to heating, said loading circuit having a camoperated switch arranged to prevent the loading of wet grain afterelapse of a predetermined time in the control cycle thus permittingample remaining time in the cycle for all wet grain then in the bin tobe thoroughly conditioned.

2. The combination according to claim I wherein said plurality of dryingbin temperature regulating circuits includes successively operatingfirst, second, and third circuits whose thermostats define threesuccessively lower temperature levels.

3. The combination according to claim 2 wherein the switches of saidfirst, second, and third drying bin temperature regulating circuitsinclude first and second single pole double throw cam actuated switches,said first single pole double throw switch when in a first positionclosing the first drying bin temperature regulating circuit and openinga circuit leading to a second single pole double throw switch, and whenin a second position opening said first heater temperature regulatingcircuit andclosing the said circuit leading to the second single poledouble throw switch, the second single pole double throw switch when ina first position closing a second drying bin temperature regulatingcircuit and opening a third drying bin temperature regulating circuitand when ina second position opening the second drying bin temperatureregulating circuit and closing the third drying bin temperatureregulating circuit.

4. The combination according to claim 1 wherein the control systemincludes a heater time controlling circuit through which power to saiddrying bin temperature regulating circuits flows, said heater timecontrolling circuit including a heater power switch actuated by one ofthe cams to connect the heater time controlling circuit to a powersource for a predetermined time interval and then disconnect.

- 5. The combination according to claim 4 including a shunt making saidheater time controlling circuit by passable.

6. The combination according to claim 4 wherein the control system has aventilating circuit for energizing the fan, said ventilating circuitfurther including a cam actuated switch to open and close theventilating cir-.

cuit, the ventilating circuit supplying power to the heater power switchof said heater time controlling circuit and therethrou'gh to said heaterregulator so that the heater can operate only when the ventilatingcircuit is closed.

7. The combination according to claim 1 wherein said heater is energizedby a fluid fuel and said regulator is an electro mechanical transducerresponsive to said temperature regulating circuits to control fuel flowthrough a valve to supply said fluid fuel to the heater at a pluralityof different rates to thereby establish and maintain a plurality ofdifferent heating levels defined by the temperature regulating electriccircuits.

8. The combination according to claim 1 wherein said control systemincludes a recycle switch located in the drying bin and a clockcontrolling thermostat, the recycle switch closing when the grainlevelin the bin reaches'the switch, said recycle switch electricallyconnected to a thermal time delay relay arranged to trigger the releaseof a cam shaft permitting a switch actuated by a cam on the cam shaft toenergize the clock controlling thermostat, said clock controllingthermostat closing to energize the clock'motor when a predetermineddrying temperature is reached thereby permitting a timed heating periodto commence when the bin reaches the said predetermined dryingtemperature.

9. The combination according to claim 8 wherein said clock controllingthermostat is shunted to permit the clock motor to have full control ofthe heating period.

10. A grain dryer having a control cycle for conditioning wet graincomprising:

a supporting frame;

a grain drying bin to hold a supply of wet grain to be conditioned;

a heater and fan mounted to the frame to heat and circulate air throughthe drying bin;

a loading auger system for loading grain into the drying bin;

a clock drive including a clock motor and a plurality of cams rotatablycoupled to the clock motor for rotation thereby;

circuit means including switches operated by said cams for controllingoperation of said heater and fan; a loading circuit responsive to saidclock drive and responsive to the level of grain in the dryer andcontrolling said loading auger system to load grain into the bin duringthe control cycle so that additional grain is loaded as the grain in thedrying bin shrinks in response to heating, said loading circuit having aclock drive controlled cam operated switch arranged to prevent theloading of wet grain after elapse of a predetermined time in the controlcycle, said fan and heater circuit means continuing operation of saidfan and heater for a predetermined time after said loading circuit hasbeen interrupted thus permitting ample remaining time in the cycle forall wet grain then in the bin to be thoroughly conditioned.

11. The combination according to claim 10 wherein the cam operatedswitch is a single pole double throw switch which energizes andde-energizes the said switch energizing said loading circuit when infirst position.

12. The combination according to claim 11 wherein said loading circuitincludes a relay operated switch which remains in an open condition whenthe clock drive is energized.

13a The combination according to claim 10 wherein said switch alsoenergizes said loading circuit when in a second position.

14. A grain dryer having a control cycle for conditioningwet graincomprising:

a supporting frame;

a grain drying bin attached to the frame to hold a supply of wet grainto be conditioned;

a heater and fan adjacent the drying bin to circulate air therethrough;

a clock drive including a plurality of cams rotatably coupled to theclock drive for rotation thereby;

a plurality of drying bin temperature regulating electric circuits, eachcircuit including a thermostat and a switch activated by one of the camsto close and open the circuit at predetermined times in the controlcycle, each regulating circuit maintaining a predetermined drying bintemperature level defined by its thermostat when the switch is closedand the circuit energized; and

heater regulator responsive to the said regulating circuits to vary heatoutput of the heater so as to maintain predetermined temperature levelsdefined by the temperature regulating electric circuits therebyproviding a plurality of different drying bin temperature levels forconditioning grain.

15. The combination according to claim 14 and further including a clockcontrolling thermostat for sensing the temperature at the drying bin andarranged to close a circuit supplying electrical power to the clockmotor when a predetermined temperature is sensed, so a timed heatingperiod is commenced by the clock motor after a given amount of grainconditioning has already occurred during the time elapsing for the binto reach the said predetermined temperature.

16. A grain dryer having a control cycle for conditioning wet graincomprising:

a supporting frame; I

a grain drying bin attached to the frame to hold a supply of wet grainto be conditioned;

a heater and fan adjacent the drying bin to circulate air therethrough;

a plurality of drying bin temperature regulating electric circuits, eachcircuit including a thermostat and a switch to be activated to close andopen the circuit at predetermined stages in the control cycle, eachregulating circuit maintaining a predetermined drying bin temperaturelevel defined by its thermostat when the switch is closed and thecircuit is energized; heater regulator responsive to the said regulatingcircuits to vary heat output of the heater so as to maintainpredetermined temperature levels defined by the temperature regulatingelectric circuits thereby providing a plurality of different drying bintemperature levels for conditioning grain; and

means to operate said switches of the temperature regulating circuitsafter the heated air has been circulated through the grain in the binfor a time to dry the grain and then change the temperature level of theair circulated through the grain.

17. The grain dryer according to claim 16 and including a plenum throughwhich the heated air from the fan 'travels to the grain drying bin, saidthermostats of the bin temperature regulating electric circuit beingdisposed in said plenum to sense the temperatures of the air at thepredetermined drying bin temperature levels.

* l =0 I I! i

1. A grain dryer having a control cycle for conditioning wet graincomprising: a frame; a grain drying bin attached to the frame to hold asupply of wet grain to be conditioned; a heater and fan mounted to saidframe to heat and circulate air through the drying bin; a clock driveincluding at least one clock motor and a plurality of cams rotatablycoupled to the clock motor for rotation thereby; a plurality of dryingbin temperature regulating electric circuits, each circuit including athermostat and a switch actuated by one of the cams to close and openthe circuit at predetermined times in the control cycle, each regulatingcircuit maintaining a predetermined drying bin temperature level definedby the thermostat in the circuit when the switch is closed and thecircuit energized; and a heater regulator responsive to the saidregulating circuits to vary heat output of the heater so as to maintainpredetermined temperature levels defined by the temperature regulatingelectric circuits; a loading auger system for loading grain into thedrying bin; and a loading circuit responsive to said clock drive andcontrolling said loading auger system to load grain into the bin duringthe control cycle so that additional grain is loaded as the grain in thedrying bin shrinks in response to heating, said loading circuit having acam operated switch arranged to prevent the loading of wet grain afterelapse of a predetermined time in the control cycle thus permittingample remaining time in the cycle for all wet grain then in the bin tobe thoroughly conditioned.
 2. The combination according to claim 1wherein said plurality of drying bin temperature regulating circuitsincludes successively operating first, second, and third circuits whosethermostats define three successively lower temperature levels.
 3. Thecombination according to claim 2 wherein the switches of said first,second, and third drying bin temperature regulating circuits includefirst and second single pole double throw cam actuated switches, saidfirst single pole double throw switch when in a first position closingthe first drying bin temperature regulating circuit and opening acircuit leading to a second single pole double throw switch, and when ina second position opening said first heater temperature regulatingcircuit and closing the said circuit leading to The second single poledouble throw switch, the second single pole double throw switch when ina first position closing a second drying bin temperature regulatingcircuit and opening a third drying bin temperature regulating circuitand when in a second position opening the second drying bin temperatureregulating circuit and closing the third drying bin temperatureregulating circuit.
 4. The combination according to claim 1 wherein thecontrol system includes a heater time controlling circuit through whichpower to said drying bin temperature regulating circuits flows, saidheater time controlling circuit including a heater power switch actuatedby one of the cams to connect the heater time controlling circuit to apower source for a predetermined time interval and then disconnect. 5.The combination according to claim 4 including a shunt making saidheater time controlling circuit by passable.
 6. The combinationaccording to claim 4 wherein the control system has a ventilatingcircuit for energizing the fan, said ventilating circuit furtherincluding a cam actuated switch to open and close the ventilatingcircuit, the ventilating circuit supplying power to the heater powerswitch of said heater time controlling circuit and therethrough to saidheater regulator so that the heater can operate only when theventilating circuit is closed.
 7. The combination according to claim 1wherein said heater is energized by a fluid fuel and said regulator isan electro mechanical transducer responsive to said temperatureregulating circuits to control fuel flow through a valve to supply saidfluid fuel to the heater at a plurality of different rates to therebyestablish and maintain a plurality of different heating levels definedby the temperature regulating electric circuits.
 8. The combinationaccording to claim 1 wherein said control system includes a recycleswitch located in the drying bin and a clock controlling thermostat, therecycle switch closing when the grain level in the bin reaches theswitch, said recycle switch electrically connected to a thermal timedelay relay arranged to trigger the release of a cam shaft permitting aswitch actuated by a cam on the cam shaft to energize the clockcontrolling thermostat, said clock controlling thermostat closing toenergize the clock motor when a predetermined drying temperature isreached thereby permitting a timed heating period to commence when thebin reaches the said predetermined drying temperature.
 9. Thecombination according to claim 8 wherein said clock controllingthermostat is shunted to permit the clock motor to have full control ofthe heating period.
 10. A grain dryer having a control cycle forconditioning wet grain comprising: a supporting frame; a grain dryingbin to hold a supply of wet grain to be conditioned; a heater and fanmounted to the frame to heat and circulate air through the drying bin; aloading auger system for loading grain into the drying bin; a clockdrive including a clock motor and a plurality of cams rotatably coupledto the clock motor for rotation thereby; circuit means includingswitches operated by said cams for controlling operation of said heaterand fan; a loading circuit responsive to said clock drive and responsiveto the level of grain in the dryer and controlling said loading augersystem to load grain into the bin during the control cycle so thatadditional grain is loaded as the grain in the drying bin shrinks inresponse to heating, said loading circuit having a clock drivecontrolled cam operated switch arranged to prevent the loading of wetgrain after elapse of a predetermined time in the control cycle, saidfan and heater circuit means continuing operation of said fan and heaterfor a predetermined time after said loading circuit has been interruptedthus permitting ample remaining time in the cycle for all wet grain thenin the bin to be thoroughly conditioned.
 11. The combination accordingto claim 10 wherein the cam operatEd switch is a single pole doublethrow switch which energizes and de-energizes the said switch energizingsaid loading circuit when in first position.
 12. The combinationaccording to claim 11 wherein said loading circuit includes a relayoperated switch which remains in an open condition when the clock driveis energized.
 13. The combination according to claim 10 wherein saidswitch also energizes said loading circuit when in a second position.14. A grain dryer having a control cycle for conditioning wet graincomprising: a supporting frame; a grain drying bin attached to the frameto hold a supply of wet grain to be conditioned; a heater and fanadjacent the drying bin to circulate air therethrough; a clock driveincluding a plurality of cams rotatably coupled to the clock drive forrotation thereby; a plurality of drying bin temperature regulatingelectric circuits, each circuit including a thermostat and a switchactivated by one of the cams to close and open the circuit atpredetermined times in the control cycle, each regulating circuitmaintaining a predetermined drying bin temperature level defined by itsthermostat when the switch is closed and the circuit energized; and aheater regulator responsive to the said regulating circuits to vary heatoutput of the heater so as to maintain predetermined temperature levelsdefined by the temperature regulating electric circuits therebyproviding a plurality of different drying bin temperature levels forconditioning grain.
 15. The combination according to claim 14 andfurther including a clock controlling thermostat for sensing thetemperature at the drying bin and arranged to close a circuit supplyingelectrical power to the clock motor when a predetermined temperature issensed, so a timed heating period is commenced by the clock motor aftera given amount of grain conditioning has already occurred during thetime elapsing for the bin to reach the said predetermined temperature.16. A grain dryer having a control cycle for conditioning wet graincomprising: a supporting frame; a grain drying bin attached to the frameto hold a supply of wet grain to be conditioned; a heater and fanadjacent the drying bin to circulate air therethrough; a plurality ofdrying bin temperature regulating electric circuits, each circuitincluding a thermostat and a switch to be activated to close and openthe circuit at predetermined stages in the control cycle, eachregulating circuit maintaining a predetermined drying bin temperaturelevel defined by its thermostat when the switch is closed and thecircuit is energized; a heater regulator responsive to the saidregulating circuits to vary heat output of the heater so as to maintainpredetermined temperature levels defined by the temperature regulatingelectric circuits thereby providing a plurality of different drying bintemperature levels for conditioning grain; and means to operate saidswitches of the temperature regulating circuits after the heated air hasbeen circulated through the grain in the bin for a time to dry the grainand then change the temperature level of the air circulated through thegrain.
 17. The grain dryer according to claim 16 and including a plenumthrough which the heated air from the fan travels to the grain dryingbin, said thermostats of the bin temperature regulating electric circuitbeing disposed in said plenum to sense the temperatures of the air atthe predetermined drying bin temperature levels.